A non-volatile memory, as one kind of various memories, has the advantage of that the stored data would not disappear after power down, and thus can be deemed as a data storage device such as a hard disk. It is distinguished from mainstream flash by the use of silicon nitride(Si3N4) instead of polysilicon for the charge storage material. SONOS promises lower programming voltages and higher program/erase cycle endurance than polysilicon-based flash.
As shown in FIG. 1, a NVM with SONOS memory cells includes a substrate 104 with a surface 116, which is divided into a memory area 106 having several NVM transistors 126; and a logic area 108 having several metal-oxide-semiconductor (MOS) transistors 112 and 114. One NVM transistor 126 is constructed by an ONO structure 136 and gate 150 The ONO structure 136 includes a tunnel dielectric layer 128, a plurality of charge trapping layers 130a and 130b, and a blocking oxide layer 138, which are stacked together one by one. The MOS transistors 112 and 114 are constructed by the gate oxide layers 140/146 and the gates 152/154, respectively.
In the conventional manufacture process of a non-volatile memory (NVM), the ONO structure 136 is formed before the formation of the gate oxide layer 140/146. Accordingly, the blocking oxide layer 138 might be lost in the following process, which will worsen the thickness control of the blocking oxide layer 138, and thus negatively influence the stability of the voltage operation.
Furthermore, since the elements in the memory area 106 and the logic area 108 will be manufactured simultaneously, there might be SiN resided within the ONO structure 136 of the memory area 104 after the etching process of the gate conductive layer of the logic area 108, which will influence the quality of the product.
Moreover, in a batch manufacturing process, the nitride of the exposed ONO structure will inhibit the growth of the oxide layer in the logic area 108, which will also cause thickness control problems.
Therefore, to solve the above-mentioned problems will be the main object of the invention.